1. Field of the Invention
This invention relates to a method of producing carbon nanostructures for use as catalyst supports in fuel cells
2. Discussion of the Prior Art
During the last few years, carbon nanostructures such as nanofibers and single or multi-walled nanotubes have received a lot of attention in the field of fuel cell research and development. The surface area, porosity and electromagnetic properties of such structures make them more suitable as catalyst supports in fuel cell electrode assemblies than carbon black powders.
Proton exchange membrane fuel cells (PEMFCs) have the highest power density when compared to other types of fuel cells. In order to improve fuel cell performance, reactant and catalytic material utilization must be optimized. PEMFCs rely on carbon-supported catalysts to produce the electrochemical reaction that generates such high power densities. In order to improve the electrochemical reaction rate, the catalyst should be as highly dispersed and as small as possible to expose the greatest surface area to the reactants. The catalyst layer usually consists of platinum crystallites with a mean diameter of a few nanometers highly dispersed on the surface of an amorphous carbon black powder.
One of the best catalyst performances in recent past was with a Pt loading of 0.1 to 0.2 mg/cm2 for 20 wt. % Pt/C [see Z. Qi et al, J. Power Sources, 113, pp. 37-43 (2003)]. Recently, it was shown by T. Yoshitake et al [see Physica B, 323, pp. 124-126 (2002)] that using single walled carbon nanohorns instead of carbon black increases the power density of PEMFCs by improving catalyst dispersion, and that iron can be used instead of or with Pt as a catalyst at the cathode of PEMFCs [see H. Wang et al, J. Phys. Chem. B, 103 pp 2042-2049 (1999) and T. Todat et al, J. Electrochem. Chem., 460, pp 258-262 (1999)]. In general, methods used to produce carbon nanostructures are somewhat complicated. Accordingly, there is a need for a simple method of producing carbon nanostructures for use as fuel cell catalyst supports.